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Scientists have identified two substances in licorice that kill the oral bacteria that cause tooth decay and gum disease. In "Isoflavonoids and Coumarins from Glycyrrhiza uralensis: Antibacterial Activity against Oral Pathogens and Conversion of Isoflavans into Isoflavan-Quinones during Purification," which appeared in the December issue of the American Chemical Society's Journal of Natural Products, licoricidin and licorisoflavan A were found to have strong antibacterial activity.
According to the researchers, practitioners of Traditional Chinese medicine use dried licorice root to treat ailments such as respiratory and digestive problems.
The researchers conducted a phytochemical investigation of a supercritical fluid extract of Glycyrrhiza uralensis, which led to the isolation of 20 known isoflavonoids and coumarins, and glycycarpan, a new pterocarpan. The presence of two isoflavan-quinones, licoriquinone A and licoriquinone B, in a fraction subjected to gel filtration was due to suspected metal-catalyzed oxidative degradation of licoricidin and licorisoflavan A.
The major compounds in the extract, as well as licoriquinone A, were evaluated for their ability to inhibit the growth of several major oral pathogens. Licoricidin and licorisoflavan showed a notable inhibition of the cariogenic species Streptococcus mutans and Streptococcus sobrinus at 10 μg/mL and the periodontopathogenic species Porphyromonas gingivalis (at 5 μg/mL) and Prevotella intermedia (at 5 μg/mL for licoricidin and 2.5 μg/mL for licorisoflavan A). In addition, licoricidin moderately inhibited growth of Fusobacterium nucleatum at the highest concentration tested (10 μg/mL).
It is hypothesized by the researchers that these substances could find significant benefit in oral care to treat or prevent oral infections.